Flexible molded polyurethane foam requires mechanical crushing to open the foam cells and prevent shrinkage. Prevention of shrinkage results in improved dimensional stability. Current mechanical methods for cell opening consist mainly of crushing, vacuum rupture or time pressure release. However, these methods usually result in incomplete or inconsistent cell opening and require the foam producer to invest in additional labor and machinery. A chemical method for cell opening which can be incorporated into the foam production process is therefore preferred.
Current chemical methods for cell opening have drawbacks such as requiring high amounts of additive (often as high as 1-5 parts per hundred parts polyol) or adversely affecting the physical properties of the foam. Some examples of current chemical methods for cell opening of polyurethane foam are described below:
U.S. Pat. No. 4,211,849 (Kollmeier et al., 1980) discloses a process for producing an open-celled polyurethane foam by mixing a polyol with a polyisocyanate, a catalyst, a blowing agent, and a crystalline polyhydroxy crosslinker, such as sorbite, mannite, trimethylolmelamine, and glucose, having at least 3 hydroxy groups.
U.S. Pat. No. 4,751,253 (Tylenda, 1988) discloses the use of an additive comprising an ester reaction product of a long chain acid with polyethylene or polypropylene glycols and/or containing free acid to produce an open celled, dimensionally stable, flexible urethane foam product.
U.S. Pat. No. 4,929,646 (Nichols et al., 1990) discloses high molecular weight, high functionality poly(oxyethylene) compounds as cell openers and softeners. The compounds are reported to be highly effective in opening the cells of foam based on PIPA polyols and in softening foams made from MDI-based polyisocyanates.
U.S. Pat. No. 5,039,713 (Petrella, 1991) and U.S. Pat. No. 5,057,480 (Petrella, 1991) disclose blowing reaction catalysts for the production of polyurethane foams. The tertiary amine catalysts consisting essentially of 25 to 80 wt % pentamethyldiethylenetriamine and 20 to 75 wt % bis(dimethylaminopropyl)methylamine are reported to provide cell opening of the foam resulting in improved breathability.
EP 471,260 (1992) discloses a process for the production of open-cell, flexible polyurethane foam in which organic acids, such as benzoic, salicylic, or adipic, or an alkali metal salt of the acid is used as an additive.
U.S. Pat. No. 5,192,812 (Farris et al., 1993) discloses the use of siloxane-oxyalkylene copolymers as cell openers in the production of urethane foams, when employed in combination with silicone surfactants.
U.S. Pat. No. 5,489,618 (Gerkin, 1996) discloses the use of an amine salt, formed by the reaction between a tertiary amine and a carboxylic acid having hydroxyl functional groups, for producing polyurethane foams. The amine salt reportedly produces foams which either are more open or more easily opened, or both, and have a reduced tendency to shrink.
U.S. Pat. No. 5,807,958 (Diblitz et al., 1998) discloses alkaline metal and alkaline earth metal salts of alkyl and alkenyl succinic acids as catalyst for making polyurethane foam. The catalysts are reported to have a favorable influence on the cell structure of the foam.